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    <div class="refentry" id="refract">
      <div class="titlepage"/>
      <div class="refnamediv">
        <h2>Name</h2>
        <p>refract — calculate the refraction direction for an incident vector</p>
      </div>
      <div class="refsynopsisdiv">
        <h2>Declaration</h2>
        <div class="funcsynopsis">
          <table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">
            <tr>
              <td>
                <code class="funcdef">genType <strong class="fsfunc">refract</strong>(</code>
              </td>
              <td>genType <var class="pdparam">I</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>genType <var class="pdparam">N</var>, </td>
            </tr>
            <tr>
              <td> </td>
              <td>float <var class="pdparam">eta</var><code>)</code>;</td>
            </tr>
          </table>
          <div class="funcprototype-spacer"> </div>
        </div>
      </div>
      <div class="refsect1" id="parameters">
        <h2>Parameters</h2>
        <div class="variablelist">
          <dl class="variablelist">
            <dt>
              <span class="term">
                <em class="parameter">
                  <code>I</code>
                </em>
              </span>
            </dt>
            <dd>
              <p>
                    Specifies the incident vector.
                </p>
            </dd>
            <dt>
              <span class="term">
                <em class="parameter">
                  <code>N</code>
                </em>
              </span>
            </dt>
            <dd>
              <p>
                    Specifies the normal vector.
                </p>
            </dd>
            <dt>
              <span class="term">
                <em class="parameter">
                  <code>eta</code>
                </em>
              </span>
            </dt>
            <dd>
              <p>
                    Specifies the ratio of indices of refraction.
                </p>
            </dd>
          </dl>
        </div>
      </div>
      <div class="refsect1" id="description">
        <h2>Description</h2>
        <p>
            For a given incident vector <em class="parameter"><code>I</code></em>, surface normal <em class="parameter"><code>N</code></em> and ratio of
            indices of refraction, <em class="parameter"><code>eta</code></em>, <code class="function">refract</code> returns the refraction vector,
            <em class="parameter"><code>R</code></em>.
        </p>
        <p>
            <em class="parameter"><code>R</code></em> is calculated as:
        </p>
        <p>
            </p>
        <pre class="programlisting">    k = 1.0 - eta * eta * (1.0 - dot(N, I) * dot(N, I));
    if (k &lt; 0.0)
        R = genType(0.0);       // or genDType(0.0)
    else
        R = eta * I - (eta * dot(N, I) + sqrt(k)) * N;</pre>
        <p>
        </p>
        <p>
            The input parameters <em class="parameter"><code>I</code></em> and <em class="parameter"><code>N</code></em> should be normalized in order to achieve the desired result.
        </p>
      </div>
      <div class="refsect1" id="versions">
        <h2>Version Support</h2>
        <div class="informaltable">
          <table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">
            <colgroup>
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              <col style="text-align: center; " class="lastvers"/>
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            <thead>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; ">
                 
            </th>
                <th style="text-align: center; border-bottom: 2px solid ; " colspan="2">
                <span class="bold"><strong>OpenGL ES Shading Language Version</strong></span>
            </th>
              </tr>
              <tr>
                <th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>Function Name</strong></span>
            </th>
                <th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">
                <span class="bold"><strong>1.00</strong></span>
            </th>
                <th style="text-align: center; border-bottom: 2px solid ; ">
                <span class="bold"><strong>3.00</strong></span>
            </th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td style="text-align: left; border-right: 2px solid ; ">refract (genType)</td>
                <td style="text-align: center; border-right: 2px solid ; ">✔</td>
                <td style="text-align: center; ">✔</td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1" id="seealso">
        <h2>See Also</h2>
        <p>
            <a class="citerefentry" href="dot.xhtml"><span class="citerefentry"><span class="refentrytitle">dot</span></span></a>,
            <a class="citerefentry" href="reflect.xhtml"><span class="citerefentry"><span class="refentrytitle">reflect</span></span></a>
        </p>
      </div>
      <div class="refsect1" id="Copyright">
        <h2>Copyright</h2>
        <p>
            Copyright <span class="trademark"/>© 2011-2014 Khronos Group.
            This material may be distributed subject to the terms and conditions set forth in
            the Open Publication License, v 1.0, 8 June 1999.
            <a class="link" href="http://opencontent.org/openpub/" target="_top">http://opencontent.org/openpub/</a>.
        </p>
      </div>
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